As a default Leave requests are sent to the Department Boss, but this can be overridden on an individual employee basis by setting their Approver.
So if, for example you have someone in a department that needs leave approving by a person other than the departmental boss, this can be set in that users setting specifically. As below:
USERS > (select the appropriate user) > PROFILE
This works particularly well for department bosses themselves, they may have the authority to approve their team members leave, but their own might have to be approved by a more senior manager or business Director.
The email notifications of a request for time off only go to the departmental boss or nominated approver.
Special Privileges for Admin Users:
Although someone designated as an admin user will not receive the email notifications or leave requests (unless they are department boss too). They will have the ability to approve leave for any employee. This helps for cover in the event a department boss is on leave and also so they can monitor outstanding leave requests.